A buckle including a plug (male member) and a socket (female member) is used as a means for coupling cord members. The plug includes a base portion having a mounting portion to mount a cord member and a pair of arm portions extending from one end of the base portion. The socket includes a body portion in a flatly tubular shape having a cavity to house the arm portions of the plug and a pair of openings to expose the tips of the arm portions of the plug from the body portion is provided on both side faces of the body portion. The plug and the socket are freely removably locked by the openings provided on both side faces of the body portion of the socket and so the buckle is called a side release buckle.
WO 2012/066615 A1 (Patent Literature 1) describes an example of a front and back engaging buckle that attaches and detaches a male member and a female member by engaging/releasing a convex engaging portion provided on the front side and the back side of a tip portion of a leg of the male member with/from an engaged portion provided in a predetermined position of an inner wall face of the body portion of the female member.
However, a front and back engaging buckle as described in Patent Literature 1 may have a complex shape, which makes it difficult to mold the buckle. Thus, a side engaging buckle that engages and releases the plug and the socket using an inclined plane or a protrusion protruded in an outer direction from both side faces of the leg of the plug has been widely used as a buckle having a simpler configuration.
U.S. Pat. No. 5,794,316 A (Patent Literature 2) has been known as an example of the side engaging buckle. In Patent Literature 2, a V-shaped stop member is provided inside the female member and also a V-shaped hook face is provided in the leg of the male member. The male member and the female member are freely removably coupled by inserting the leg of the male member into the female member to engage/release the V-shaped stop member with/from the V-shaped hook face on both side faces of the female member.